1. Field of the Invention
An electromagnetic flowmeter includes at least one electromagnetic coil arranged outside a liquid flow passage for generating an electromotive force in the liquid flow, and at least one pair of electrodes adjustably extending into the liquid flow for generating a velocity component signal. Preferably, two collinearly arranged coils are provided externally on opposite sides of the liquid passage, and a first set of two orthogonally-arranged pairs of coplanar electrodes are mounted on an adjustable probe strut that extends into the liquid flow. For greater accuracy, a Hall-effect device may be provided on the probe. Additional sets of electrode pairs may be secured to the strut in planes parallel to the first electrode set. Three orthogonally-arranged velocity components are achieved by using a second pair of collinear coils mounted externally of the liquid passage in orthogonally displaced relation relative to the first pair of coils.
2. Description of Related Art
The Faraday Law of electromagnetic induction has been applied to water flow measuring devices for nearly 100 years. As early as 1910, a device for measuring the speed of a moving vessel was patented. Since then, a multitude of other applications and devices utilizing the Faraday Law have followed. Devices were made for measuring the volumetric flow in both open channels and full pipes where the magnetic field was applied to a large portion of the flow cross section and the induced electromotive force (emf) was averaged over an equally large portion of the cross section. Additionally, probe type velocity sensors were invented where the magnetic field was localized to a small area (generally the size of the probe) and the sensing electrodes were attached to the surface of the probe allowing for the measurement of water velocities in the vicinity of the probe.
As described in the following patents, the construction of probe type velocity sensors were focused on trying to make the best velocity measurement while keeping the magnet and electrode assembly from adversely affecting the flow around the sensor thereby affecting the velocity measurement. The Olson U.S. Pat. No. 3,693,440 describes ‘an “open” cage-like housing for the magnetic field coils and electrodes that practically eliminates any physical interference with the water flow. Additional patents, such as Cushing U.S. Pat. No. 4,089,218, Marsh U.S. Pat. Nos. 4,459,858 and 4,688,432, all describe various probe type electromagnetic sensors. In all of the prior art, the electrodes and the magnetic coils were rigidly fixed in relationship to each other. Even in the Marsh U.S. Pat. Nos. 5,398,552 and 6,598,487, where the magnet assembly and the electrode assembly were separable, the magnet and electrodes were secured at a known relationship to each other when placed together for the flow measurement.
The present invention described herein differs from the prior art in that the electrodes are separate from the magnetic coil assembly, and the magnetic coil assembly is placed at some distance from the electrodes, preferably out of the path of the flowing water.